I thought I would write a bit more about the strategy of undermining your own political party’s leadership, and why I think it is daft even on its own terms
One of the characteristics of a few on the far left of politics is a total belief in the ends they strive for, and very little concern about the means used to achieve it. Anything that brings on the revolution is OK. We now seem to have some near the centre of the political spectrum behaving in exactly the same way. Their revolution is deposing Corbyn from the leadership of the Labour party, and undermining that leadership is their means. For the sake of clarity, let me call this group the anti-Corbynistas.
When someone loses a leadership election, they generally retire gracefully. Sometimes they are offered a senior role under the new leader (Clinton and Obama) and become an active supporter. On other occasions (David and Ed) they would prefer, for whatever reason, to withdraw from the scene. And normally their supporters do the same. The goal of getting the party re-elected overrides any thoughts about who might have been a better leader. Other parties and the media will do their best to exploit these past divisions, but nearly everyone in the party avoids this bait.
As far as the contestants for the 2015 Labour party leadership are concerned, they have played by these rules. One chose to be in the Shadow Cabinet, and the two that declined have not spent their free time writing critical articles in the media. The majority of Labour MPs have made a similar choice: work with the new leadership or stay quiet. But an important minority, accompanied by a large group of political commentators, have not. They are the anti-Corbynistas.
Their mantra is the impossibility of Labour led by Corbyn winning.  This has the same status as a belief in the inevitability of revolution: just as the latter is fed by every injustice, so the former is supported by every opinion poll. For that reason I do not want to try and contest the certainty of their belief - there is no point. Instead I want to question the logic of what then follows.
Their reasoning goes like this. Because Corbyn is a barrier to Labour winning, the prime goal must be to hasten his departure by any means. As these individuals have easy access to the media, their main means is to criticise, or even mock, the Labour leadership at every turn. By doing this they ensure that Corbyn’s defeat at the polls will be sooner or greater, and thereby they believe hasten his removal from power.
What I want to argue that this tactic is counterproductive. Just as the behaviour of the revolutionary makes most sensible people doubt the attraction of any revolution, so the constant sniping at the leadership extends rather than shortens its life.
The reason is straightforward. Corbyn was elected by the membership, and if anything support for him has grown since then. (This and subsequent statements are based on this poll.) On key issues like Trident this membership share Corbyn’s own views, although it is worth noting that most expect their MP to represent their constituents views rather than their own.  So the question you have to ask is what will persuade Labour members to vote for someone else.
The obvious answer is a gradual realisation that Corbyn cannot win a general election, together with the emergence of someone else who looks like a better bet.  The mistake the anti-Corbynistas make is to then think that their tactics of open criticism will hasten this process. 
In fact the tactic will have the opposite effect. If they kept quiet and Corbyn loses in elections badly, as they are sure he will, then Labour members will see quite clearly the need for change and look elsewhere. By constantly generating bad publicity for the party, they muddy these waters. Corbyn supporters will claim that the bad results are the result of anti-Corbynista activity, and it will not be obvious they are wrong. So if anything the tactic of the anti-Corbynistas will delay, rather than hasten, the day that the membership elects someone else. That is why people like Tony Blair should tell them to stop.
If their strategy is so obviously misguided, why do the anti-Corbynistas persist? One reason may be human nature: they hate Corbyn, and find it difficult to bite their tongue. Another is that they are constantly cheered on or goaded by the right, although you might imagine that would worry some people. But there is an alternative and more rational reason. Their real goal may not be the overthrow of Corbyn, but the creation of a new party. That strategy within the UK system is also flawed, but that would have to be the subject of another post.
Why am I, a macroeconomist, writing about such a political issue? I get annoyed by their constant references to me as a Corbyn supporter because I consort with the enemy, but I can live with that. (The same would come from the right anyway.) What annoys me more is that they are playing a large role in depriving the UK of an effective opposition party. Every time the new leadership launches a justified criticism of the current government, there is a fair chance this will turn into a discussion of divisions within Labour.
This is in danger of influencing macro policy. Osborne’s fiscal charter - which involves going for surplus - is so isolated in terms of informed opinion and out of tune with current concerns that it deserves to be ridiculed at every turn, so that if nothing else it is not tried again. I think that could happen with concerted pressure, but that pressure needs to include a united opposition. This did not happen before the election because Labour seemed to want to avoid the subject. We then had McDonnell for a moment flirting with the idea of supporting the charter. Now that Labour appear to have decided on a more sensible strategy, it would be tragic if this opposition to Osborne was diluted by some within Labour seeming to support the charter and dishing their own side.
 Some argue that these people are really a fifth column that should not be in the Labour party at all. I think this is wrong. Their belief that Corbyn is a barrier to Labour winning seems perfectly genuine to me, and I think Labour needs to be a broad church.
 Another part of the anti-Corbynista’s mantra is that Corbyn’s goal is to take control of the party by deselecting MPs, and there are examples of individuals who do indeed want that, but this poll suggests it is not what most party members want.
 Sometimes anti-Corbynistas complain that Labour party members would prefer to lose than compromise with the electorate: that does not seem true, but it also rather obviously contradicts their own strategy.
 In comments to this blog I have had some anti-Corbynistas deny this disloyalty has any effect on the electorate: again this seems very dubious but also contradicts the strategy.